Police say nothing significant was found on Monday in the search for the four people that have been missing in Foveaux Strait since Thursday.
A fishing vessel, the Easy Rider, sank after being hit by a large wave, leaving eight people presumed dead and one survivor.
Police suspended the full-scale search for the missing people on Sunday, but continued with a limited search on Monday.
A helicopter searched along the mainland coast between Waipapa Point and Riverton on Monday afternoon, where tides and currents suggest bodies of the missing would come ashore.
Police say there was no sign of the missing four.
The Transport Accident Investigation Commission is winding up its initial interviews, but plans to come back next week to interview relatives of the missing once they have had space to hold tangi, or ceremonies ahead of burials.
Maritime New Zealand also has an investigation team in Bluff, but says it has not yet decided whether it will open a full, separate inquiry.
A private search was also conducted on Monday and includes relatives of the people who were on the boat. It will concentrate on an area off Stewart Island where the vessel sank.
The Transport Accident Investigation Commission says a report into the Easy Rider's sinking will determine whether it needs to make any urgent safety recommendations.
Spokesperson Peter Northcote says over the weekend the commission interviewed the survivor and collated evidence.
Mr Northcote told Radio New Zealand's Morning Report programme on Monday the inquiry will take about a year to complete.
"We are particularly interested in any new learnings that might come from an incident.
"There is plenty of information out there that people involved in the marine industry can take on board to operate as safely as possible - things like lifejackets, reporting, other lifesaving equipment."
Mr Northcote says if the commission learns anything new it can make an urgent safety recommendation before its report is released.
Call for boaties to be more careful
The operator of the Bluff Fisherman's Radio says boaties need to change their ways to avoid more tragedies.
Meri Leask says the skippers of small boats in particular need to make sure someone knows where they have gone and to always wear life jackets.
Ms Leask says Foveaux Strait can appear deceptively safe and she often sees boaties taking unnecessary risks.